1. Field of the Invention
This invention relates to a light-ignitable thyristor which consists of a main and an auxiliary thyristor (amplifying gate), integrated for ignition boosting, wherein the anode base zone of the light-ignitable thyristor reaches up to the surface on the cathode side in a narrow duct so that the PN junction formed by the anode base zone and the cathode base zone also borders directly the surface on the cathode side, and wherein the cathode zone of the auxiliary thyristor is surrounded by a ring-shaped gate zone of the main thyristor and in contact therewith.
2. Description of the Prior Art
Such light-ignitable thyristors as noted above are, for example, known from the German Pat. No. 24 08 079. In case of these known thyristors, the narrow duct of the anode base zone bordering the surface on the cathode side is arranged within a cathode zone of the auxiliary thyristor designed in the shape of a ring. This is followed towards the outside by the gate zone of the main thyristor, which contacts it, and both zones together are enclosed by the cathode zone of the main thyristor. When the surface on the cathode side is radiated by light, the auxiliary thyristor is firstly ignited which then effects the ignition of the main thyristor through the gate zone.
In the case of these known light-ignitable thyristors, the ignition sensitivity of the auxiliary thyristor is designed at as high a level as possible with a given dU/dt resistance which leads to a relatively small cathode zone. This results in a high ignition ratio Z without any special measures. In this context, the ratio ##EQU1## is called the ignition ratio. This ratio is about between 30 and 100 for light-ignitable thyristors with a high sensitivity to light. Therefore, a relatively large current must be supplied by the auxiliary thyristor for the ignition of the main thyristor which, with a high di/dt, can lead to the destruction of the auxiliary thyristor.